About 20 % of all foodstuffs produced in the world are wasted because of septic action by microorganisms and many people have experienced bad health effects due to the ingestion of septic food. Since many microorganisms have been reported as putrefactive and pathogenic bacteria, which cause the septic action of food, the prevention of bacteria contamination in food storage is one of the most important factors for supplying safe and healthy food to the consumer. The authors have screened a psychrotrophic bacterium, RT102 strain, which synthesized an antimicrobial violet pigment, from the intestine of a rainbow trout and found out that the violet pigment shows an antimicrobial action for some species of microorganisms. The chemical structure and antimicrobial activity of violet pigment produced by the psychrotrophic bacterium isolated from the intestine of a rainbow trout were investigated experimentally. The psychrotrophic bacterium was found to be a new species belonging to the genus Janthinobacterium lividum. ィイD11ィエD1H, ィイD113ィエD1C-NMR, and FT-MS spectra analyses results showed that the chemical structure of violet pigment was a mixture of vioracein and deoxyvioracein. The antimicrobial activity of violet pigment was confirmed for putrefactive bacteria such as Bacillus subtilis, Bacillus megaterium, Staphylococcus aureus, and Pseudomonas aeruginosa. The growth inhibitory and lethal effects of violet pigment on the putrefactive bacteria were evaluated by increasing the concentration of violet pigment, ranging from 5 to 20 mg/1. It was found that higher concentrations of violet pigment caused not only growth inhibition but also the death of the putrefactive bacteria.